When attempting to render from Sequencer in a portrait aspect ratio, something seems to be wrong with the frustum culling. I do not think it has adapted to the aspect ratio, as it seems to stay in a landscape aspect ratio.
Attached is a zip file with the map + sequencer file. I rendered it using the Movie Render Queue (must enable plugin). I’m also attaching the settings and results.
CesiumforUnrealSamples.zip (153.2 KB)

All I did was change the aspect ratio of the sensor on the camera, and then specify an output resolution in the movie render queue settings.
